1. Field of the Invention
The present invention relates to a motor drive controller and a method for detecting rotation state.
2. Description of the Related Art
In the related art, there is a motor drive controller of a position sensor-less type that detects rotational position of a rotor based on an induced voltage of a motor instead of detecting the rotational position by a position sensor. The motor drive controller of the position sensor-less type generates a phase signal (pulse signal) by comparing an induced voltage appearing at a motor terminal in an open section (non-energized phase) with a reference voltage (equivalent neutral point electric potential) using a comparator and detects the rotational position of the rotor based on this phase signal.
In JP-A-H7-337080, an air conditioner is described which changes an activation method of a fan motor based on the rotation state thereof when the fan motor rotates according to an external disturbance such as a blowing wind. The air conditioner described in JP-A-H7-337080 determines whether or not the rotation direction of the motor is a forward direction by making a collation of rotor magnetic pole position detection signals corresponding to three phases in which a rotor magnetic pole position detection signal (generated by comparing an induced voltage (hereinafter, referred to as a “counter-electromotive voltage”) of a coil with a neutral voltage) having an electrical angle of a 180° width is prepared for one phase and rotor magnetic pole position detection signals are prepared in the same way for the other two phases and rotor magnetic pole position signal patterns in the rotation direction at the time of driving the fan motor set in a rotation number setting circuit in advance. However, in a control process of comparing a counter-electromotive voltage and a neutral voltage of a coil with each other, due to generation of an insufficient counter-electromotive voltage, it is difficult to detect the counter-electromotive voltage at the time of startup and at the time of a low rotation speed.
In JP-A-2011-120421, a motor control device is described which includes a motor startup controller that, at the time of starting up a motor, executes closed loop control, in which all-phase opening for opening all the phase coils described above and set duty drive are repeated, executes detection of a rotation state, which is one state of forward rotation, stop, reverse rotation, of a sensorless brushless motor, based on detection of a voltage zero cross between a counter-electromotive force during the opening of all the phases and comparison reference electric potential and transits to the process of current control according a phase at which the sensorless brushless motor is in the forward rotation based on a determined result of the detection of the rotation state. The motor control device described in JP-A-2011-120421, at the time of starting up the motor, executes the closed loop control, in which all-phase opening for opening all the phase coils and the set duty drive are repeated, and detects the rotation direction of the motor based on a detection of a voltage zero cross between a counter-electromotive voltage at the time of opening all the phases and a comparison reference voltage. In other words, a voltage zero cross is detected during an extremely low rotation speed that is forcibly caused at the time of startup, and the rotation direction is detected based on the signal.
However, the motor control device described in JP-A-2011-120421 may have the following problems. In the detection of a rotation direction, since the rotation direction is determined through monitoring of an elapse of a change in the counter-electromotive voltage during a predetermined period, there are cases where it is difficult to make detection according to condition of the magnitude and the time of an external disturbance such as a blowing wind. In addition, it is necessary to execute the closed loop control at the time of start-up, and accordingly, there is a problem in that the control process becomes complicated.